In the related art, regarding an inductive load control device connected to a DC power supply to control an inductive load such as a motor, means for detecting a failure of its own constituent elements such as a protection circuit at the time of reverse connection of the DC power supply is proposed. For example, JP-A-2012-065405 discloses a motor control device intended to diagnose whether or not reverse connection protection means for protecting a circuit included in the motor control device in a case where a power supply is reversely connected has failed. The motor control means includes reverse connection protection means which includes a switching element that connects or disconnects a battery and a motor and a backflow prevention element for preventing from backflow of a current when the battery is reversely connected, and failure diagnosis means for diagnosing failure of the reverse connection protection means. The failure diagnosis means calculates a difference between a cutoff potential difference before connecting the reverse connection protection means and a connection potential difference when connecting the reverse connection protection means and compares the calculated difference with a threshold value which is set in advance. When the difference is equal to or larger than the threshold value, it is determined that the reverse connection protection means has not failed, and when the difference is smaller than the threshold value, it is determined that the reverse connection protection means has failed.
JP-A-2012-188101 discloses a control device for an electric power steering apparatus which is intended to reliably detect a failure of a MOS-FET and can determine a failure of a parasitic diode even in a case where the MOS-FET is used for a power supply relay. In this electric power steering apparatus, MOS-FETs including a built-in parasitic diode and connected in series in a reverse direction and a capacitor located on an output side of a MOS-FET at the subsequent stage thereof are disposed in an energizing path between a battery and a motor drive circuit. In a state immediately after an ignition switch is turned on, the MOS-FETs are controlled to be turned on or off in a predetermined order, and a failure of the MOS-FET and the parasitic diode is detected based on an output voltage of each MOS-FET.